Lap joints are defined for purposes herein as joints between two parallel surfaces. The traditional way of forming a lap joint is simply that of driving a fastener, e.g. nails, staples, brads, screws and the like through one of the materials and into the other material to be joined. In certain constructions, however, it is not desired that the fastener be driven through one or both of the materials to be joined. For example, when conventional wallboard is placed on wooden studs by driving nails therethrough, the indentations created by the nail heads must be spackled and sanded smooth, thus, increasing the labor required for such construction. Similarly, in forming a lap joint between wood paneling and wall studs, driving nails through the wood paneling leaves and unsightly appearance. The use of finishing nails decreases the obtrusiveness of the nail heads, but the appearance of the panel is, nonetheless, marred. To avoid this difficulty, the very time consuming method of towing the finishing nails into the panel is often employed. In yet another example, when container pallets are constructed, lap joints formed by nailing the plates to the stringers allow the nailheads to contact containers on the pallet, e.g. paper bags and the like, with the result that some of the containers are damaged. Continued use of such nailed pallets can also result in the plates being dislodged from the stringer and failure of the pallet.
Thus, as has been long recognized in the art, there are many constructions which ideally utilize fasteners which are referred to as "hidden fasteners". These fasteners, in general, have securing projections from both sides of a plate so that the projections may be driven into both members of the lap joint and secure the two together. Hidden fasteners of this nature, however, have several inherent difficulties. As can be easily appreciated, since the projections must not penetrate through one of the two members, for certain lap joints the projections must be relatively short in length, e.g. securing wallboard and wooden paneling to wall studs. The relatively short projections, and without a keeping device such as a nail head, substantially reduce the resistance to separation of the two members. If the number of projections is simply increased, the chances of splitting or disintegrating one or both of the members of the lap joint is substantially increased, particularly in connection with wallboard and thin paneling.
As can also be appreciated, since the projections must be driven into at least one of the members of the lap joint by applying a pressure to one of the members, the chances of marring one or both of the members is substantially increased. Accordingly, the amount of force required to cause penetration of a projection into at least one of the members must be kept as low as possible in order to minimize such marring. This is of particular concern in soft or crushable materials, such as wallboard and soft wall paneling.
Further, in certain materials the chances of splitting or crushing the material substantially increases with the number of projections which must penetrate the material. Again, this is particularly true with materials such as wall paneling or crushable material such as wallboard. Under these circumstances, simply increasing the number of projections to increase the strength of the lap joint is not acceptable.
Accordingly, it would be substantial benefit to provide fasteners of a type described above, but where these fasteners may be used in these more exacting applications. It would be a further advantage in the art if such fasteners could also provide relatively strong lap joints, even in thin and crushable materials, and without substantially marring those materials.